1. Field of the Invention
The present invention generally relates to a magnetic tape cassette for use with a digital audio tape recorder (DAT) or the like and, more particularly, is directed to a magnetic tape cassette in which a slider can be reliably engaged with a lower cassette part at a predetermined position.
2. Description of the Prior Art
Conventional tape recorders such as a digital audio tape recorder (DAT) or the like employ a magnetic tape cassette which is generally depicted by reference numeral 11 in FIGS. 1 to 3, for example.
As illustrated, in the case of the magnetic tape cassette for the DAT, a magnetic tape T is protected not only by upper and lower cassette parts 2, 3 but also by a lid 7, a slider 8 or the like in order to prevent a drop-out from occurring in a reproduced signal when the surface of the magnetic tape T is smudged by fingermarks, oily components, dust or the like.
A pair of reel hubs 5a, 5b around which the magnetic tape T is wound is accommodated within a cassette housing 4 that is composed of the upper cassette shell or part 2 and the lower cassette shell or part 3 which are fastened together by some suitable means such as screws or the like. A transparent window 2a is formed on the upper cassette part 2 so that the user can visually confirm the remaining amount of the magnetic tape T wrapped around the reel hubs 5a and 5b. Also, in order to prevent the magnetic tape T from being exposed through a mouth portion 6 of the cassette housing 4 when the magnetic tape cassette 11 is not in use or when the magnetic tape cassette 11 is preserved, a lid 7 is pivotally attached to the front portion of the cassette housing 4 such that the lid 7 becomes freely rotatable in the upper direction. The lid 7 is constantly spring-biased by a spring (not shown) in the direction in which the lid closes the mouth portion 6.
The slider 8 is provided on the lower cassette part 3 so that it slides along the lower cassette part 3 back and forth (in the directions shown by arrows a and b in FIGS. 2A, 2B) to thereby open and close the mouth portion 6. The slider 8 has bored therethrough a pair of reel shaft insertion apertures 8b, 8b that communicate with a pair of reel shaft insertion apertures 3b, 3b bored through the lower cassette part 3 at the opening position of the mouth portion 6. The slider 8 is constantly spring-biased by a slider spring S in the forward direction (in the arrow a direction (see FIG. 2A) in which the slider 8 closes the mouth portion 6) relative to the lower cassette part 3.
When the magnetic tape cassette 11 thus arranged is not in use, as shown in FIG. 2A, the lid 7 closes the front portion of the mouth portion 6 and the slider 8 closes the lower portion of the mouth portion 6, whereby the magnetic tape T extended within the mouth portion 6 is isolated from the outside. The reel shaft insertion apertures 3b of the lower cassette part 3 and the reel shaft insertion apertures 8b of the slider 8 are not coincident with one another and the slider 8 closes the reel shaft insertion apertures 3b of the lower cassette part 3, thereby preventing the inside of the cassette housing 4 from being smudged by dust or the like.
When the magnetic tape cassette 11 is loaded onto a recording and reproducing apparatus such as the DAT or the like, as shown in FIG. 2B, the slider 8 is slid rearward of the cassette housing 4 (in the arrow b direction) and then held. Also, the lid 7 is rotated upwardly to open the front portion and the lower surface of the mouth portion 6.
Under this condition, a tape loading guide member (not shown) on the recording and reproducing apparatus side can be inserted into the mouth portion 6 of the cassette housing 4. Also, the reel shaft insertion apertures 8b, 8b of the slider 8 become coincident with the reel shaft insertion apertures 3b, 3b of the lower cassette half 3, whereby reel shafts (not shown) of the recording and reproducing apparatus can be inserted into the reel shaft insertion apertures 3b, 8b. 
When the magnetic tape cassette 11 is not in use, the slider 8 is moved forwardly and held at the position at which the slider closes the mouth portion 6. When the magnetic tape cassette 11 is loaded onto the recording and reproducing apparatus, the slider 8 is moved backwardly and then held at the position at which the slider opens the mouth portion 6. In order to hold the slider 8 at the respective predetermined positions, two pairs of engagement apertures 8c, 8c and 8d, 8d are bored through the slider 8 at two positions in the arrow b direction in FIG. 2B and a pair of slider lock portions 3c, 3c of pin-configuration that can be engaged with the engagement apertures 8c, 8c and 8d, 8d are formed on the lower cassette part 3.
As shown in FIGS. 1 and 3, the slider lock portions 3c, 3c are formed by cutting one portion of the lower cassette part 3. These slider lock portions 3c, 3c have a spring-biasing property so that the respective engagement protrusions 3d, 3d formed on the tops thereof are constantly spring-biased so as to return to the direction in which the engagement protrusions 3d, 3d are engaged with the engagement apertures 8c or 8d of the slider 8. In order to prevent the returning force of the slider lock portions 3c, 3c from being reduced when the lower cassette part 3 is deformed by the deterioration of the material forming the lower cassette part 3, it is proposed that compression coil springs (hereinafter referred to as slider lock springs) 9, 9 be respectively interposed between the engagement protrusions 3d, 3d of the slider lock portions 3c, 3c and the upper cassette part 2.
FIG. 3 of the accompanying drawings shows an example of the slider lock spring 9 that the assignee of the present application has previously proposed (see Japanese Patent Application No. 3-48741). As shown in FIG. 3, the slider lock spring 9 comprises a spring body portion 9a formed of a coil spring whose inner diameter is progressively increased upwardly and an elongated portion 9b that is linearly elongated from the upper end edge of the spring body portion 9a. The coil spring is doubly wound around only the upper and lower end portions tightly.
In the slider lock springs 9, 9 thus arranged, the spring body portions 9a, 9a are wound around a pair of pins 2b, 2b protruded from the inner side surface of the upper cassette part 2 in response to the inner surface sides of the tops of the engagement protrusions 3d, 3d of the slider lock portions 3c, 3c. The elongated portion 9b is welded (fixed by a caulking process) to a recess 2d of a fixed portion 2c of the upper cassette part 2. Therefore, the slider lock springs 9, 9 can be prevented from disenging from the upper cassette part 2 and come in contact with the inner end faces of the engagement protrusions 3d, 3d of the slider lock portions 3c, 3c to downwardly press the engagement protrusions 3d, 3d, thereby reinforcing the spring-biasing force of the slider lock portions 3c, 3c. 
The above conventional magnetic tape cassette 11, however, suffers from the following disadvantages:
That is, if the spring-biasing force of the slider lock spring 9 is increased, although the returning force of the slider lock portion 3c is reinforced more effectively, a force (opening force) that is required to open the slider 8 must be increased because the top end faces of the respective engagement protrusions 3d are brought in parallel contact with the respective engagement apertures 8c when the engagement protrusions 3d of the slider lock portions 3c are disengaged from the engagement apertures 8c of the slider 8.
There is then the antinomy that, while the spring-biasing force of the slider lock spring 9 cannot be set to a too large a value, the small spring-biasing force of the slider lock spring 9 cannot achieve a reinforcing effect of the slider lock portion 3 sufficiently, thereby locking the slider 8 in the unstable locked condition.
Moreover, the above conventional magnetic tape cassette cannot overcome the shortcomings which follow:
Welding fixing by the caulking process) the slider lock spring on the upper cassette part is not advantageous in conformability when the magnetic tape cassette is assembled by machines or the like.
When the slider lock spring is of a tight-winding type, a difference between the inner diameter of the slider lock spring and the outer diameter of the pin on the upper cassette part can be reduced so that the slider lock spring can be fitted into the pin with a small pressure. Since the difference between the inner diameter of the slider lock spring and the outer diameter of the pin on the upper cassette half is set to be small, such difference is not suitable for mounting the slider lock spring that is hard to deform at the tight-winding portion of the slider lock spring.
Therefore, it is an object of the present invention to provide an improved magnetic tape cassette in which the aforesaid shortcomings and disadvantages encountered with the prior art can be eliminated.
More specifically, it is an object of the present invention to provide a magnetic tape cassette in which a force required to open a slider can be suppressed to be small while a spring-biasing force for reinforcing a slider block portion can be set to be large.
It is another object of the present invention to provide a magnetic tape cassette in which a slider lock spring can be fitted into a pin with a small pressure.
It is still another object of the present invention to provide a magnetic tape cassette in which a slider lock spring can be easily assembled on an upper cassette part by an automatic assembling apparatus.
It is a further object of the present invention to provide a magnetic tape cassette which is suitable for use with a digital audio tape recorder (DAT) or the like.
As a first aspect of the magnetic tape cassette according to the present invention, in order that a slider, slidably attached to a lower cassette part so as to open and close a mouth portion of a cassette housing, be locked at a predetermined position, a slider lock portion is provided on the lower cassette part, an engagement aperture that is engaged with the slider lock portion is bored through the slider and a spring is interposed between the slider lock portion and an upper cassette part to thereby spring-bias the slider lock portion in the direction in which the slider lock portion is fitted into the engagement aperture. This magnetic tape cassette further includes an inclined portion having a configuration tapered toward a cassette housing being formed on one end face of the engagement aperture bored through the slider which opposes the top of the slider lock portion of the lower cassette part.
As a second aspect of the magnetic tape cassette according to the present invention, in order to lock a slider slidably attached to a lower cassette part at a predetermined position, a slider lock spring, that is fitted into a pin projected from an upper cassette part, is interposed between the slider lock portion provided on the lower cassette part and the upper cassette part to thereby spring-bias the slider lock portion in the direction in which the slider lock portion is fitted into the engagement aperture. In this magnetic tape cassette, at least one end portion of the slider lock spring is bent toward the inside of a coil winding portion to form a pin supporting portion.
The above-mentioned and other objects, features, and advantages of the present invention will become apparent from the following detailed description of illustrative embodiments thereof to be read in conjunction with the accompanying drawings, in which like reference numerals are used to identify the same or similar parts in the several views.